In recent years, attempts have been made to improve the amount of hot mix asphalt products that get recycled. Conventional direct-fired prior art drum hot mix asphalt plants often utilize a mixture of virgin aggregate and RAP. Typically, a mixture of about 20% RAP and 80% virgin aggregate is considered aggressive use of RAP.
The virgin aggregate material is used to prevent the RAP from sticking to the HMA plant components and building up to cause blockages and inefficient operation. The virgin aggregate is also included to indirectly heat the RAP.
While there has been much desire to increase the amount of RAP used each year in HMA applications, and the percentage of RAP used nationally in HMA applications has been increasing since the early days of RAP, difficulties exist with increasing the percentage content of RAP in HMA. Often too much RAP in an HMA mix will result in clogging up the HMA drum or burning of the RAP or both.
Consequently, there exists a need for improved methods and systems for cost effectively increasing the RAP content of HMA in an environmentally sound manner.